Early Eocene Nummulitids from Gebel Umm Russeies, El Galala El Bahariya, Eastern Desert, Egypt

Seven larger foraminiferal species: Nummulites aff. nemkovi SCHAUB, 1966, Nummulites partschi DE LA HARPE, 1880, Nummulites bassiounii BOUKHARY & BLONDEAU, 1991, Nummulites cf. campesinus SCHAUB, 1966, Assilina aff. major HEIM, 1908, Decrouezina aegyptiaca Boukhary, 1994 and Operculina sp. are described from the Early Eocene Gebel Umm Russeies, Northern Galala, Eastern Desert, Egypt. These taxa are biostratigraphically evaluated and according to the standard shallow benthic zones, the identifi ed biozones span SBZ 10 to SBZ 12 in the shallow benthic zones (SBZ) of SERRA-KIEL et al. (1998) which are assigned to the Late Ypresian.


INTRODUCTION
El Galala El Bahariya is a high fl at topped plateau located be tween latitudes 28°50' N and 29°45' N and longitudes 31°40' E and 32°30' E and is one of the most impressive topographical features in the northern part of the north Eastern Desert. The plateau overlooks the Gulf of Suez rising 977 m above sea level at Gebel Umm Russeies, and extends between 50 km south of Suez city in the north and Wadi Araba in the south, a distance of about 60 km. Inland, the plateau stretches westwards where it merges into the Mokattam plateau overlooking Cairo in the west. The El Galala El Bahariya plateau is cut by some wadis, but the main tributaries from west to east are: Wadi El Qena, Wadi El Ghul, Wadi El-Khafouri, Wadi Abu Diaba, Wadi Ogila, El Wadi El-Abyad, Wadi Naoz, Wadi Umm Russeies and Wadi Haroz (Fig. 1). The studied area lies at the far north and east sides of El Galala El Bahariya, between latitudes 29°30' N and 29°40' N and longitudes 32°07' E and 32°25' E.
Near the North Eastern part of the El Galala Plateau, At Khashm El-Galala, Wadi Haroz and Wadi Umm Russeies, the lower part of the scarp is composed of Lower Cretaceous variegated sandstone and marl (Malha Formation), overlain by a thick series of marly limestone, marl and a thick band of dolomite of Late Cretaceous age (Galala Formation).
The following Turonian fossiliferous dolomite and conglomeratic beds (Umm Russeies Formation) are exposed and, with thickness overlain by marly limestone and shale of Palaeocene age (Esna Shale). These rocks are capped by Eocene carbonates rocks which are completely dolomitic in the east and gradually change westward to dolomitic limestone. To the west of Wadi Naoz, Eocene limestones form the foot of the scarp, Palaeocene and Cretaceous strata never crop out again west of Wadi Naoz. The general dip of the strata is towards the west and varies from 8° to 10°.
Many faults along the northern face of North Galala are arranged en echelon (Fig. 1).
El Galala El Bahariya, like other localities in the northern part of the Eastern Desert, is affected by volcanic intrusions. Sheet basalts can be seen at the top of the plateau, and also at the opening of Wadi Naoz, Wadi Umm Qena and Wadi Haroz (Fig. 1). As a consequence, the sediments are slightly metamorphosed at the contact and hence marblised limestone and calcite dykes are found at Wadi Haroz, Wadi Ghoul and Gebel Menedra.
Fi gu re 1: Geologic map of the study area and location of studied sections.
This study is based on four measured stratigraphic sections (Figs. 2-5) representing the exposed Eocene succession. A brief description and discussion of the rock units from base to top is as follows: Esna Shale Formation, Thebes Formation and Minia Formation.

The Esna Shale Formation
In the study area, the Esna Shale is composed of thinly bedded marl, marly chalk, grey-greenish to grey shale that unconformably overlies the Umm Russeies Formation (SWE-DAN et al., 1991). The base of the Esna Shale is characterized by the presence of Operculina sp. and Discocyclina sp. while This paper deals with the study of larger foraminifera, mainly nummulitids, collected from the Lower Eocene rocks of Gebel Umm Russeies in an attempt to locate their exact stratigraphic position in the frame of the standard shallow benthic zones (SBZ of SERRA-KIEL et al., 1998) of the Eocene sequence.

STRATIGRAPHICAL SETTING
The Eocene rocks are widely distributed in Egypt, well ex pos ed along the Nile Valley, Sinai Peninsula, Western Desert, and the Eastern Desert including Northern and Southern Galala. There is great lateral variation in both lithofacies and biofacies. the Morozovella velascoensis and Morozovella edgari zones are recorded higher in the sequence. The Esna Shale disappears in the western part of the study area, east of Wadi Naoz due to the regional dip. In the eastern part (W. Haroz), it consists of thinly bedded marly chalk and has a thickness of 35 m. The Esna Shale attains a thickness that ranges from 60 m at section 1 to 80 m at section 4. The microfaunal assemblages recorded in this study from the Esna Shale indicate an Ypresian age for this Unit.

The Thebes Formation
The Thebes Formation was introduced by SAID (1960) for a massive unit of limestone with fl int bands of Ypresian age. The type locality is at Gebel Gurnah, west of Luxor, near the site of the ancient Thebes Capital of Egypt, where it is about 300 m in thickness. The basal beds of this unit are rich in Operculina libyca Schwager (Operculina limestone), whi le the lower part is poor in megafossils, and is massive -thickly bedded with tabular and concretionary fl int bands. The upper part includes several marl beds alternating with nummulitic limestone bands rich in Nummulites and megafossils. The micro fossils include Nummulites praecursor and N. subramondi, Lucina thebaica, Conoclypeus delanouei, indicating an Early Eocene age for this assemblage and formation. Shale Formation. It consists of laminated to thinly bedded fi ne grained limestone and chalk with scattered chert nodules. The middle member is 100-125 m thick, thinly bedded chalk with nodular limestone interbeds, rich with large benthonic foraminifera. The upper member reaches a maximum thickness of 50 m at Gebel Shaghab. It consists of interbeds of oysterlimestone and oyster shell-debris with Alveolina limestone.
In the study area, SADEK (1926) mentioned that the Lower Eocene in El Galala El Bahariya composed of clastic sediments in the lower part, whereas its upper part is a carbonate, which is quite different from the Nile Valley sequ-ence. SAID (1962SAID ( , 1990 later stated that the Farafra Formation in the north and south Galala is rich in Alveolinid fauna of Early Eocene age.  recorded 48 m of sandy dolomitic bands rich in alveolinids, operculines and nummulitids overlying the chalky limestone of the Sudr Formation at Gebel Thelmet in the northeastern part of Southern Galala Plateau and named it the Southern Galala Formation SCHEIBNER et al. (2002).
Here, the Thebes Formation is classifi ed lithological into lower, middle and upper members based on lithological and biological characters, that are as follows: Fi gu re 5: Stratigraphic section measured south of Wadi Naoz (section no. 4).

The Lower Member:
This member is composed of whi te to pale white limestone and marl to marly limestone of yellowish white color, slightly hard, with rare chert nodules in the upper part. There are many horizons crammed with Nummulites partschi, Nummulites aff. nemkovi, small and medium sized Orbitolites and small specimens of Lucina. The thickness of this horizon ranges from 25 to 40 m and increases towards the western side of the study area. At the base of the Thebes Formation, Alveolines have been found southwest of Wadi Naoz (sections 3 and 4 respectively).
The Middle Member: This member is composed of a sequence of well bedded, white or cream limestone, with poorly lithifi ed bands of chalky to marly limestone, rich with chert bands and nodules. It is also characterized by the cyclic presence of hard bands of limestone about 30-50 cm thick, and is overlain by thinner (10-15 cm) soft bands of a chalky to marly limestone. The top part is made of chert band; each band attains a thickness of a 5 to 8 cm including Nummulites partschi and rare medium to large sized Nautilus sp. The thickness of this member ranges from 50-90 m, increasing towards the west. The maximum thickness occurs at Wadi Ogila (90 m).
The nummulitic limestone member measures about 100, 147, 115 and 132 m at sections 1, 2, 3 and 4 respectively. In the west at Wadi Oliga the member reaches its maximum thickness 160 m, whereas the thickness of this member is reduced to the East, measuring 80 m at Wadi Haroz.

The Minia Formation
In the studied area, the Minia Formation comformably overlies the Thebes Formation. It occupies the topmost part of the scarp face of El Galala El Bahariya as well as outcropping over the surface of the plateau. The formation is well exposed at Gebel Umm Russeies and extends beyond the study area. It also crops out on the western side of Wadi Naoz. The formation is composed of white to snow white limestone at the base, intercalated with dolomitic limestone in the middle which increases in thickness upwards where it is interbedded with thin beds of limestone and chalky limestone. This part of the section is very rich in larger foraminifera (Nummulites), algae and macrofossils. The following species were identifi ed from this part of the formation: Nummulites bassiounii BOUKHARY & BLONDEAU, Decrouezina aegyptiaca (CUVILLIER), Assilina aff. major HEIM, Orbitolites sp., Carolia fi scheri STROUGO, Vulsella crispata FISCHER, large size Turritella sp., Natica sp., Trochus sp. and Pterolucina monosulcata (STROUGO) and long Alveolina cf. frumentiformis.
The total thickness of this part of the sequence reaches 150 m in section 2, 90 m in section 3 and 170 m in section 4.

BIOSTRATIGRAPHY
The distribution of the different species of the larger foraminifera mainly (Nummulites and Operculina) in the studied succession of the studied area had enabled the identifi cation of 4 biostratigraphic zones. These matched well with SBZ 10 to SBZ 12 of the Standard Shallow Benthic Zones of SERRA-KIEL et al. (1998). Figure 6 shows the distribution of the larger foraminifera in the studied area and the identifi ed biostratigraphic zones, from top to base, as follows: 4. These bio zones are assigned to the Late Ypresian following the scheme of SCHAUB (1981) and SERRA-KIEL et al. (1998).

Depository:
The material is deposited in the collection of BOUKHARY, Department of Geology, Faculty of Science, Ain Shams University, Egypt. Microspheric Form (B-Form): Form lenticular or fl at, slightly irregular rounded or truncated periphery, granulation visible on the surface especially near the periphery sometimes granules arranged on or between the septal fi laments, surface with radial septal fi lament or curved diameter 6.5-13.2 mm, thickness 2.8-3.3mm.

The Morphological Characteristics of Nummulitids Taxonomy
Equatorial Section: With the characteristics of the Nummu lites partschi group, the septa are inclined, particularly near the outer marginal cord, Spire more or less regular and loosly coiled laxer toward the periphery, marginal cord relatively thick and regular, approximately, 1/5 th of the height of the whorls, septa straight and slightly curved or inclined, chamber quadrangular in the centre, while isometric in the centre becoming elongated (length greater than height) near the periphery.
Number of whorls in relation to the radius is as follows: 8 whorls in a radius of 3.5 mm, 9 whorls in a radius of 3.99 mm and 10 to 12 whorls in a radius of 5.6 to 6.72 mm.

Megalospheric Form (A-Form):
Form lenticular more or less infl ated, truncated or rounded pillars arranged around the centre. Diamater: 2.5-4.5 mm, thickness: 1.5-2.6 mm, number of whorls v. radius; 3 whorls in a radius of 1.26 mm to 1.54 mm and 4 whorls in a radius of 1.75-1.89 mm. Protoconch size ranges from 0.35 mm to 0.49 mm.

Remarks:
Our species compares well with Nummulites partschi. It differs from N. burdigalensis cantabricus SCHAUB as being much larger and loosly coiled coiling (Table 1).
Nummulites partschi as mentioned in SCHAUB (1981) has a wide distribution in the Tethyan Province and is a guide species for the Ypresian. According to SCHAUB (1981), Nummulites partschi lays in the phylogenetic series between Nummulites ornatus "Upper Ilerdian" and Nummulites tauricus DE LA HARPE (Middle to Upper Cuisian).

Stratigraphic distribution:
This species is recorded from the Thebes Formation of all the studied sections. In the stratigraphic section no. 1, it is recorded from Beds 8, 10 and 11. In the stratigraphic section 2, the species is recorded from Beds 3 and 8. In the stratigraphic section no. 3, the species is recorded from Beds 4, 8 and 9 and in the stratigraphic section no. 4 the species occurs in from Bed 12.
Equatorial Section: Spire and septa are of the same character as the Nummulites archiaci-pratti group, the curved and broadly arched number of whorls v. radius is as follows: 13 whorls in a radius of 8.68 mm, 9 and 10 mm and 14 whorls in a radius of 9.60 mm.
Megalospheric Form (A-Form): Form lenticular, fl at, septal fi laments radial to undulate. A few granules occur around the centre. Diameter ranges from 3.8 to 5.5 mm, thickness is 1-1.5 mm.
Equatorial Section: Spire and septa exhibit the characteristics of the Nummulites archiaci-pratti group, number of whorls v. radius is as follows: 3 whorls in a radius of 1.8 mm, 4 whorls in a radius of 1.8 mm and 5 whorls in a radius of 2.8 mm. Protoconch size ranges from 0.5 to 0.57 mm.
Remarks and differences: Nummulites aff. nemkovi is compares and matches well with the description and fi gures given in SCHAUB (1981) except for a small difference in thickness, which seems to be lower in the present material. It is larger than N. haymanensis and smaller than N. kaufmanni and N. distans.
Stratigraphic distribution: This species is recorded from stratigraphic section no. 1, Bed 9 and 4 and in stratigraphic section no. 2, Bed 4.
Equatorial Section: Spire regular, as in the Nummulites burdigalensiss group, test lenticular with a more or less round ed periphery, marginal cord rather thick, number of whorls v. radius is as follows: 12 whorls in a radius of 4.3 mm and 13 whorls in a radius of radius 4.6 mm.

Megalospheric Form (A-Form):
Form biconical lenticular thick in the middle of the test; surface with radial septal fi laments or curved with developing granules in the pole. Diameter ranges from 2.5-3.6 mm, thickness is 1.0-1.9 mm.
Equatorial Section: Spire as in form B is regular with the character of Nummulites burdigalensis group. Number of whorls v. radius is as follows: 5 whorls in a radius of 1.4-1.8 mm, protoconch size ranges from 0.25 to 0.35 mm.
Remarks: Nummulites cf. campesinus is a primitive stage of N. campesinus SCHAUB; it falls into the lower part of the dimensional range of this species.

Microspheric Form (B-Form):
Test of medium size, lenticular with truncated subangular margin, granulated in juveniles and non granular in adults as in this generation the granulation is a regressive feature. Septal fi laments radial, S-shaped to broadly meandering or wrinkled. Diameter rang es from 8.5 mm to 16.2 mm and thickness ranges from 3 to 6 mm.
Equatorial section: Spire regular and the septa are typical of the Nummulites subramondi group, curved at the base while perpendicular at the top. Number of whorls against the radius: 10-14 whorls in a radius of 5.5-6.25 mm and 15-17 whorls in a radius of 6.30-7.7 mm.
Megalospheric Form (A-Form): Test small, lenticular to biconical with radial septal fi laments slightly twisted at the pole. A few small granules on the pole are observed. Diameter ranges from 3.0 to 4.0 mm, thickness ranges from 1 to 2 mm. Number of whorls v. radius: 4 whorls in a radius of 1.7 to 1.89 mm. Protoconch diameter ranges from 0.49 to 0.6 mm.
Equatorial Section: In keeping with the characteristics of the Assilina spira group, the number of whorls for given radius is as follows: 8 whorls in a radius of 7.35 mm, 6.51 mm, and 6.86 mm and 9 whorls in a radius of 7.1 mm and 7.91 mm.

Megalospheric Form (A-Form):
Diameter ranges from 3.5-6.2 mm, thickness is 0.6-1.2. Number of whorls per radius is as follows: 3 whorls in a radius between 1.47-2.83 and 5 whorls in a radius of 2.975 mm, 3.08 mm, 2.94 mm, 3.01 mm and 2.94 mm. Diameter of protoconch ranges from 0.28 mm to 0.42 mm (Table 3).

Stratigraphic distribution:
This species is only recorded only from stratigraphic section no. 2, Bed 16.

Remarks:
Our species compares well with Assilina major of SCHAUB (1981).
Age: Late Ypresian. No. or whorls v. radius 8 whorls in a radius of 6.5-7.0 mm 9 whorls in a radius of 7.1-8.0 mm 10 whorls in a radius of 8.5-11.5 mm 11 whorls in a radius of 10.4-13.0 mm 12 whorls in a radius of 11.9 mm No. of whorls 8-9 whorls 10-12 whorls

Diameter Present Present
Diameter A-Form 3.5-6.2 mm 6-10 mm Thickness 0.60-1.2 mm 0.8-1.5 mm No. of whorls v. radius 3 whorls in a radius of 1.5-2.5 mm 5 whorls in a radius of 2.9-4.3 mm 5 whorls in a radius of 3.5-5.0 mm 6 whorls in a radius of 4.5-5.5 mm